The present invention relates to methods for producing thermoplastic compositions. These compositions may be used to produce multicomponent fibers. These multicomponent fibers include an unreacted mixture of an aliphatic polyester polymer as a continuous phase, polyolefin microfibers as a discontinuous phase encased within the aliphatic polyester polymer continuous phase, and a compatibilizer for the aliphatic polyester polymer and the polyolefin microfibers. The multicomponent fiber exhibits substantial biodisintegratable properties yet is easily processed.
Disposable absorbent products currently find widespread use in many applications. For example, in the infant and child care areas, diapers and training pants have generally replaced reusable cloth absorbent articles. Other typical disposable absorbent products include feminine care products such as sanitary napkins or tampons, adult incontinence products, and health care products such as surgical drapes or wound dressings. A typical disposable absorbent product generally comprises a composite structure including a liquid-permeable topsheet, a fluid acquisition layer, an absorbent structure, and a liquid-impermeable backsheet. These products usually include some type of fastening system for fitting the product onto the wearer.
Disposable absorbent products are typically subjected to one or more liquid insults, such as of water, urine, menses, or blood, during use. As such, the outer cover materials of the disposable absorbent products are typically made of liquid-insoluble and liquid impermeable materials, such as polypropylene films, that exhibit a sufficient strength and handling capability so that the disposable absorbent product retains its integrity during use by a wearer and does not allow leakage of the liquid insulting the product.
Although current disposable baby diapers and other disposable absorbent products have been generally accepted by the public, these products still have need of improvement in specific areas. For example, many disposable absorbent products can be difficult to dispose of. For example, attempts to flush many disposable absorbent products down a toilet into a sewage system typically lead to blockage of the toilet or pipes connecting the toilet to the sewage system. In particular, the outer cover materials typically used in the disposable absorbent products generally do not disintegrate or disperse when flushed down a toilet so that the disposable absorbent product cannot be disposed of in this way. If the outer cover materials are made very thin in order to reduce the overall bulk of the disposable absorbent product so as to reduce the likelihood of blockage of a toilet or a sewage pipe, then the outer cover material typically will not exhibit sufficient strength to prevent tearing or ripping as the outer cover material is subjected to the stresses of normal use by a wearer.
Furthermore, solid waste disposal is becoming an ever increasing concern throughout the world. As landfills continue to fill up, there has been an increased demand for material source reduction in disposable products, the incorporation of more recyclable and/or degradable components in disposable products, and the design of products that can be disposed of by means other than by incorporation into solid waste disposal facilities such as landfills.
As such, there is a need for new materials that may be used in disposable absorbent products that generally retain their integrity and strength during use, but after such use, the materials may be more efficiently disposed of. For example, the disposable absorbent product may be easily and efficiently disposed of by composting. Alternatively, the disposable absorbent product may be easily and efficiently disposed of to a liquid sewage system wherein the disposable absorbent product is capable of being degraded.
Although degradable monocomponent fibers are known, problems have been encountered with their use. In particular, known degradable fibers typically do not have good thermal dimensional stability such that the fibers usually undergo severe heat-shrinkage due to the polymer chain relaxation during downstream heat treatment processes such as thermal bonding or lamination.
In contrast, polyolefin materials, such as polypropylene, typically exhibit good thermal dimensional stability but also have problems associated with their use. In particular, polyolefin fibers typically are hydrophobic and, and such, exhibit poor wettability, thus limiting their use in disposable absorbent products intended for the absorption of fluids such as body fluids. Although surfactants can be used to improve the wettability of polyolefin fibers, the use of such surfactants introduces additional problems such as added cost, fugitivity or permanence, and toxicity. Furthermore, polyolefin fibers are generally not biodisintegratable or compostable.
It would therefore be desirable to prepare a biodisintegratable nonwoven material which includes fibers that exhibit the thermal dimensional stability of polyolefin materials yet are substantially biodisintegratable and are also wettable without the use of surfactants. A simple solution to this desire would be to simply mix a polyolefin material with a degradable material so as to gain the benefits of using both materials. However, the components of a multicomponent fiber generally need to be chemically compatible, so that the components effectively adhere to each other, and have similar Theological characteristics, so that the multicomponent fiber exhibits minimum strength and other mechanical and processing properties. It has therefore proven to be a challenge to those skilled in the art to combine components that meet these basic processing needs as well as meeting the desire that the entire multicomponent fiber be effectively substantially degradable and hydrophilic.
It is therefore desirable to provide a method for forming a biodisintegratable nonwoven material that includes multicomponent fibers that are substantially degradable in the environment. It is also desirable to provide a method for forming a substantially degradable multicomponent fiber that has good thermal dimensional stability and is hydrophilic without the substantial use of surfactants. Finally, it is also desirable to provide a method for forming a biodisintegratable nonwoven material having a substantially degradable multicomponent fiber which is easily and efficiently prepared and which is suitable for use in preparing these biodisintegratable nonwoven materials.
The present invention concerns a method for forming a thermoplastic composition that is substantially biodisintegratable and yet which is easily prepared and readily processable into desired final structures.
One aspect of the present invention concerns a method for forming a thermoplastic composition that includes a mixture of a first component, a second component, and a third component.
One embodiment of such a thermoplastic composition includes an unreacted mixture of an aliphatic polyester polymer as a substantially continuous phase, polyolefin microfibers as a substantially discontinuous phase encased within the aliphatic polyester polymer substantially continuous phase, and a compatibilizer for the aliphatic polyester polymer and the polyolefin microfibers.
In another aspect, the present invention concerns a method for forming a multicomponent fiber that is substantially degradable and yet which is easily prepared and readily processable into desired final structures.
One aspect of the present invention concerns a method for forming a multicomponent fiber that includes an unreacted mixture of an aliphatic polyester polymer as a substantially continuous phase, polyolefin microfibers as a substantially discontinuous phase encased within the aliphatic polyester polymer substantially continuous phase, and a compatibilizer for the aliphatic polyester polymer and the polyolefin microfibers.
One aspect of the present invention concerns a method for forming a multicomponent fiber that includes an unreacted thermoplastic mixture of an aliphatic polyester polymer as a substantially continuous phase, polyolefin microfibers as a substantially discontinuous phase encased within the aliphatic polyester polymer substantially continuous phase, and a compatibilizer for the aliphatic polyester polymer and the polyolefin microfibers as one component of the multicomponent fiber. The fiber may be in any configuration such that the thermoplastic mixture is exposed to the fiber surface as in sheath-core, eccentric sheath-core, side-by-side, or any other configuration. Such fibers could be made in to any type of nonwoven material.
In another aspect, the present invention concerns a process for preparing the biodisintegratable nonwoven material disclosed herein.
The present invention is directed to a method for forming a thermoplastic composition that may be used in the production of multi-component fibers and biodisintegratable nonwoven materials. These fibers and materials demonstrate higher contact angle hysteresis, quicker intake times, and improved skin dryness as compared to prior art nonwoven materials. In addition, these multi-component fibers and biodisintegratable nonwoven materials also exhibit high wetting rates, which is unexpected based upon the higher hysteresis values.
These methods are used to form a thermoplastic composition that includes a first component, a second component, and a third component. As used herein, the term xe2x80x9cthermoplasticxe2x80x9d is meant to refer to a material that softens when exposed to heat and substantially returns to its original condition when cooled to room temperature.
It has been discovered that, by using an unreacted mixture of an aliphatic polyester polymer as a substantially continuous phase, polyolefin microfibers as a substantially discontinuous phase encased within the aliphatic polyester polymer substantially continuous phase, and a compatibilizer for the aliphatic polyester polymer and the polyolefin microfibers, a thermoplastic composition may be prepared wherein such thermoplastic composition is substantially degradable yet which thermoplastic composition is easily processable into nonwoven structures that exhibit effective fibrous mechanical properties and liquid handling properties.
The first component in the thermoplastic composition is an aliphatic polyester polymer. Suitable aliphatic polyester polymers include, but are not limited to, poly(lactic acid), polybutylene succinate, polybutylene succinate-co-adipate, polyhydroxybutyrate-co-valerate, polycaprolactone, sulfonated polyethylene terephthalate, mixtures of such polymers, or copolymers of such polymers.
In one embodiment of the present invention, it is desired that the aliphatic polyester polymer used is poly(lactic acid). Poly(lactic acid) polymer is generally prepared by the polymerization of lactic acid. However, it will be recognized by one skilled in the art that a chemically equivalent material may also be prepared by the polymerization of lactide. As such, as used herein, the term xe2x80x9cpoly(lactic acid) polymerxe2x80x9d is intended to represent the polymer that is prepared by either the polymerization of lactic acid or lactide.
Lactic acid and lactide are known to be asymmetrical molecules, having two optical isomers referred to, respectively, as the levorotatory (hereinafter referred to as xe2x80x9cLxe2x80x9d) enantiomer and the dextrorotatory (hereinafter referred to as xe2x80x9cDxe2x80x9d) enantiomer. As a result, by polymerizing a particular enantiomer or by using a mixture of the two enantiomers, it is possible to prepare different polymers that are chemically similar yet which have different properties. In particular, it has been found that by modifying the stereochemistry of a poly(lactic acid) polymer, it is possible to control, for example, the melting temperature, melt rheology, and crystallinity of the polymer. By being able to control such properties, it is possible to prepare a multicomponent fiber exhibiting desired melt strength, mechanical properties, softness, and processability properties so as to be able to make attenuated, heat set, and crimped fibers.
It is generally desired that the aliphatic polyester polymer be present in the thermoplastic composition in an amount effective to result in the thermoplastic composition exhibiting desired properties. The aliphatic polyester polymer will be present in the thermoplastic composition in a weight amount that is less than 100 weight percent, beneficially between about 45 weight percent to about 90 weight percent, suitably between about 50 weight percent to about 88 weight percent, and more suitably between about 55 weight percent to about 70 weight percent, wherein all weight percents are based on the total weight amount of the aliphatic polyester polymer, the polyolefin microfiber, and the compatibilizer present in the thermoplastic composition. The compositional ratio of the three components in the thermoplastic composition is generally important to maintaining the substantial biodegradability of the thermoplastic composition because the aliphatic polyester polymer generally needs to be in a substantially continuous phase in order to maintain access to the biodisintegratable portion of the thermoplastic composition. An approximation of the limits of component ratios can be determined based on the densities of the components. The density of a component is converted to a volume (assume 100 g of each component), the volumes of the components are added together for a total thermoplastic composition volume and the components"" weight averages calculated to establish the approximate minimum ratio of each component needed to produce a thermoplastic composition with a volumetric majority of the aliphatic polyester polymer in the blend.
It is generally desired that the aliphatic polyester polymer exhibit a weight average molecular weight that is effective for the thermoplastic composition to exhibit desirable melt strength, fiber mechanical strength, and fiber spinning properties. In general, if the weight average molecular weight of an aliphatic polyester polymer is too high, this represents that the polymer chains are heavily entangled which may result in a thermoplastic composition comprising that aliphatic polyester polymer being difficult to process. Conversely, if the weight average molecular weight of an aliphatic polyester polymer is too low, this represents that the polymer chains are not entangled enough which may result in a thermoplastic composition comprising that aliphatic polyester polymer exhibiting a relatively weak melt strength, making high speed processing very difficult. Thus, aliphatic polyester polymers suitable for use in the present invention exhibit weight average molecular weights that are beneficially between about 10,000 to about 2,000,000, more beneficially between about 50,000 to about 400,000, and suitably between about 100,000 to about 300,000. The weight average molecular weight for polymers or polymer blends can be determined using a method as described in the Test Methods section herein.
It is also desired that the aliphatic polyester polymer exhibit a polydispersity index value that is effective for the thermoplastic composition to exhibit desirable melt strength, fiber mechanical strength, and fiber spinning properties. As used herein, xe2x80x9cpolydispersity indexxe2x80x9d is meant to represent the value obtained by dividing the weight average molecular weight of a polymer by the number average molecular weight of the polymer. In general, if the polydispersity index value of an aliphatic polyester polymer is too high, a thermoplastic composition comprising that aliphatic polyester polymer may be difficult to process due to inconsistent processing properties caused by polymer segments comprising low molecular weight polymers that have lower melt strength properties during spinning. Thus, it is desired that the aliphatic polyester polymer exhibits a polydispersity index value that is beneficially between about 1 to about 15, more beneficially between about 1 to about 4, and suitably between about 1 to about 3. The number average molecular weight for polymers or polymer blends can be determined using a method as described in the Test Methods section herein.
In the present invention, it is desired that the aliphatic polyester polymer be biodegradable. As a result, the resulting nonwoven material, including the aliphatic polyester polymer, will be substantially degradable when disposed of to the environment and exposed to air and/or water. As used herein, xe2x80x9cbiodegradablexe2x80x9d is meant to represent that a material degrades from the action of naturally occurring microorganisms such as bacteria, fungi, and algae. Using biodegradable materials permits the formation of biodisintegratable materials. As used herein, xe2x80x9cbiodisintegratablexe2x80x9d is meant to represent that a portion of the nonwoven material biodegrades, leaving an amount of material that is not able to be seen by the unaided eye.
In the present invention, it is also desired that the aliphatic polyester polymer be compostable. As a result, nonwoven material including the aliphatic polyester polymer will be substantially compostable when disposed of to the environment and exposed to air and/or water. As used herein, xe2x80x9ccompostablexe2x80x9d is meant to represent that a material is capable of undergoing biological decomposition in a compost site such that the material is not visually distinguishable and breaks down into carbon dioxide, water, inorganic compounds, and biomass, at a rate consistent with known compostable materials.
The second component of the thermoplastic composition made by the present invention is polyolefin microfibers. Polyolefins are known to those skilled in the art. Any polyolefin capable of being fabricated into an article, such as a microfiber, is believed suitable for use in the present invention. Exemplary of polyolefins suitable for use in the present invention are the homopolymers and copolymers comprising repeating units formed from one or more aliphatic hydrocarbons, including ethylene, propylene, butene, pentene, hexene, heptene, octene, 1,3-butadiene, and 2-methyl-1,3-butadiene. The polyolefins may be high or low density and may be generally linear or branched chain polymers. Methods of forming polyolefins are known to those skilled in the art.
Polyolefins, such as those described above, are generally hydrophobic in nature. As used herein, the term xe2x80x9chydrophobicxe2x80x9d refers to a material having a contact angle of water in air of at least 90 degrees. In contrast, as used herein, the term xe2x80x9chydrophilicxe2x80x9d refers to a material having a contact angle of water in air of less than 90 degrees. For the purposes of this application, contact angle measurements may be determined as set forth in Robert J. Good and Robert J. Stromberg, Ed., in xe2x80x9cSurface and Colloid Sciencexe2x80x94Experimental Methodsxe2x80x9d, Vol. II, (Plenum Press, 1979), pages 63-70.
It is generally desired that both the aliphatic polyester polymer and the polyolefin be melt processable. It is therefore desired that the aliphatic polyester polymer and the polyolefin exhibit a melt flow rate that is beneficially between about 1 gram per 10 minutes to about 200 grams per 10 minutes, suitably between about 10 grams per 10 minutes to about 100 grams per 10 minutes, and more suitably between about 20 grams per 10 minutes to about 40 grams per 10 minutes. The melt flow rate of a material may be determined according to ASTM Test Method D1238-E incorporated in its entirety herein by reference.
In the present invention, the polyolefin is used in the form of a microfiber. As used herein, the term xe2x80x9cmicrofiberxe2x80x9d is meant to refer to a fibrous material having a diameter that is less than about 50 micrometers, beneficially less than about 25 micrometers more beneficially less than about 10 micrometers, suitably less than about 5 micrometers, and most suitably less than about 1 micrometer.
In one embodiment of the present invention, the polyolefin microfiber comprises a percentage of the cross sectional area of a multicomponent fiber prepared from the thermoplastic composition of the present invention that is effective for the multicomponent fiber to exhibit desirable melt strength, fiber mechanical strength, and fiber spinning properties. In general, if the polyolefin microfiber comprises a percentage of the cross sectional area of a multicomponent fiber that is too high, this generally results in a nonwoven material that will not be substantially biodisintegratable or that will be difficult to produce. Conversely, if the polyolefin microfiber comprises a percentage of the cross sectional area of a multicomponent fiber that is too low, this generally results in a nonwoven material that will not exhibit effective structural properties or that may be difficult to process. Thus, the polyolefin microfiber desirably comprises a percentage of the cross sectional area of a multicomponent fiber that is beneficially less than about 20 percent of the cross sectional area of the multicomponent fiber, more beneficially less than about 15 percent of the cross sectional area of the multicomponent fiber, and suitably less than about 10 percent of the cross sectional area of the multicomponent fiber.
As used herein, the term xe2x80x9cfiberxe2x80x9d or xe2x80x9cfibrousxe2x80x9d is meant to refer to a material wherein the length to diameter ratio of such material is greater than about 10. Conversely, a xe2x80x9cnonfiberxe2x80x9d or xe2x80x9cnonfibrousxe2x80x9d material is meant to refer to a material wherein the length to diameter ratio of such material is about 10 or less.
The polyolefin is generally desired to be in the form of a microfiber so as to allow the polyolefin to effectively function as a structural support within the thermoplastic composition so as to prevent a substantial thermal dimensional-shrinkage of the thermoplastic composition during processing while generally maintaining a desired degree of substantial biodegradability of the thermoplastic composition.
It is generally desired that the polyolefin microfibers be present in the thermoplastic composition in an amount effective to result in the thermoplastic composition exhibiting desired properties. The polyolefin microfibers will be present in the thermoplastic composition in a weight amount that is beneficially between greater than 0 weight percent to about 45 weight percent, suitably between about 5 weight percent to about 40 weight percent, and more suitably between about 10 weight percent to about 30 weight percent, wherein all weight percents are based on the total weight amount of the aliphatic polyester polymer, the polyolefin microfiber, and the compatibilizer present in the thermoplastic composition. It is generally important for the polyolefin to be a substantially discontinuous phase of the thermoplastic composition so that the polyolefin microfibers can provide structural support to the thermoplastic composition or materials formed from the thermoplastic composition, such as fibers or nonwovens, without negatively affecting the biodegradability of the aliphatic polyester or of the substantial biodegradability of the thermoplastic composition or materials formed from the thermoplastic composition.
Either separately or when mixed together, the aliphatic polyester polymer and the polyolefin microfiber are generally hydrophobic. However, it is generally desired that the thermoplastic composition used in the present invention, and nonwoven materials prepared from the thermoplastic composition, generally be hydrophilic so that such materials are useful in disposable absorbent products which are insulted with aqueous liquids such as water, urine, menses, or blood. Thus, it has been found desirable to use another component as a surfactant in the thermoplastic composition of the present invention in order to achieve the desired hydrophilic properties.
Furthermore, it has been found desirable to improve the processability of the aliphatic polyester polymer and the polyolefin microfibers, since such polymers are not chemically identical and are, therefore, somewhat incompatible with each other which tends to negatively affect the processing of a mixture of such polymers. For example, the aliphatic polyester polymer and the polyolefin microfibers are sometimes difficult to effectively mix and prepare as an essentially homogeneous mixture on their own. Generally, then, it has been found desirable to use a compatibilizer to aid in the effective preparation and processing of the aliphatic polyester polymer and the polyolefin microfibers into a single thermoplastic composition.
Therefore, the third component in the thermoplastic composition is a compatibilizer for the aliphatic polyester polymer and the polyolefin microfibers. Compatibilizers suitable for use in the present invention will generally comprise a hydrophilic section which will generally be compatible to the aliphatic polyester polymer and a hydrophobic section which will generally be compatible to the polyolefin microfibers. These hydrophilic and hydrophobic sections will generally exist in separate blocks so that the overall compatibilizer structure may be di-block or random block. It is generally desired that the compatibilizer initially functions as a plasticizer in order to improve the preparation and processing of the thermoplastic composition. It is then generally desired that the compatibilizer serves as a surfactant in a material processed from the thermoplastic composition, the nonwoven material of the present invention, by modifying the contact angle of water in air of the processed material. The hydrophobic portion of the compatibilizer may be, but is not limited to, a polyolefin such as polyethylene or polypropylene. The hydrophilic portion of the compatibilizer may contain ethylene oxide, ethoxylates, glycols, alcohols or any combinations thereof. Examples of suitable compatibilizers include UNITHOX(copyright)480 and UNITHOX(copyright)750 ethoxylated alcohols, or UNICID(copyright) Acid Amide Ethoxylates, all available from Petrolite Corporation of Tulsa, Okla.
It is generally desired that the compatibilizer exhibit a weight average molecular weight that is effective for the thermoplastic composition to exhibit desirable melt strength, fiber mechanical strength, and fiber spinning properties. In general, if the weight average molecular weight of a compatibilizer is too high, the compatibilizer will not blend well with the other components in the thermoplastic composition because the compatibilizer""s viscosity will be so high that it lacks the mobility needed to blend. Conversely, if the weight average molecular weight of the compatibilizer is too low, this represents that the compatibilizer will generally not blend well with the other components and have such a low viscosity that it causes processing problems. Thus, compatibilizers suitable for use in the present invention exhibit weight average molecular weights that are beneficially between about 1,000 to about 100,000, suitably between about 1,000 to about 50,000, and more suitably between about 1,000 to about 10,000. The weight average molecular weight for a compatibilizer material can be determined using methods known to those skilled in the art.
It is generally desired that the compatibilizer exhibit an effective hydrophilic-lipophilic balance ratio (HLB ratio). The HLB ratio of a material describes the relative ratio of the hydrophilicity of the material. The HLB ratio is calculated as the weight average molecular weight of the hydrophilic portion divided by the total weight average molecular weight of the material, which value is then multiplied by 20. If the HLB ratio value is too low, the material will generally not provide the desired improvement in hydrophilicity. Conversely, if the HLB ratio value is too high, the material will generally not blend into the thermoplastic composition because of chemical incompatibility and differences in viscosities with the other components. Thus, compatibilizers useful in the present invention exhibit HLB ratio values that are beneficially between about 10 to about 40, suitably between about 10 to about 20, and more suitably between about 12 to about 18.
It is generally desired that the compatibilizer be present in the thermoplastic composition in an amount effective to result in the thermoplastic composition exhibiting desired properties. In general, a minimal amount of the compatibilizer will be needed to achieve an effective blending and processing with the other components in the thermoplastic composition. In general, too much of the compatibilizer will lead to processing problems of the thermoplastic composition. The compatibilizer will be present in the thermoplastic composition in a weight amount that is beneficially between about 3 weight percent to about 25 weight percent, more beneficially between about 10 weight percent to about 25 weight percent, suitably between about 12 weight percent to about 20 weight percent, and more suitably between about 13 weight percent to about 18 weight percent, wherein all weight percents are based on the total weight amount of the aliphatic polyester polymer, the polyolefin microfiber, and the compatibilizer present in the thermoplastic composition.
While the principal components of the thermoplastic composition have been described in the foregoing, such thermoplastic composition is not limited thereto and can include other components not adversely effecting the desired properties of the resulting biodisintegratable nonwoven materials. Exemplary materials which could be used as additional components would include, without limitation, pigments, antioxidants, stabilizers, surfactants, waxes, flow promoters, solid solvents, plasticizers, nucleating agents, particulates, and materials added to enhance processability of the thermoplastic composition. If such additional components are included in a thermoplastic composition, it is generally desired that such additional components be used in an amount that is beneficially less than about 5 weight percent, more beneficially less than about 3 weight percent, and suitably less than about 1 weight percent, wherein all weight percents are based on the total weight amount of the aliphatic polyester polymer, the polyolefin microfiber, and the compatibilizer present in the thermoplastic composition.
The thermoplastic composition made by the present invention is generally the resulting morphology of a mixture of the aliphatic polyester polymer, the polyolefin polymer, the compatibilizer, and, optionally, any additional components. The polyolefin polymer forms a substantially discontinuous phase encased within the aliphatic polyester polymer substantially continuous phase. To achieve the desired properties for the thermoplastic composition, it is desirable that the aliphatic polyester polymer, the polyolefin microfibers, and the compatibilizer remain substantially unreacted with each other. As such, each of the aliphatic polyester polymer, the polyolefin microfibers, and the compatibilizer remain distinct components of the thermoplastic composition. Furthermore, it is desired that the aliphatic polyester polymer forms a substantially continuous phase and that the polyolefin microfibers form a substantially discontinuous phase, wherein the aliphatic polyester polymer continuous phase substantially encases the polyolefin microfibers within its structure. As used herein, the term xe2x80x9cencasexe2x80x9d, and related terms, are intended to mean that the aliphatic polyester polymer continuous phase substantially encloses or surrounds the polyolefin microfibers.
In one embodiment of the present invention, after dry mixing together the aliphatic polyester polymer, the polyolefin polymer, and the compatibilizer to form a thermoplastic composition dry mixture, such thermoplastic composition dry mixture is beneficially agitated, stirred, or otherwise blended to effectively uniformly mix the aliphatic polyester polymer, the polyolefin polymer, and the compatibilizer such that an essentially homogeneous dry mixture is formed. The dry mixture may then be melt blended in, for example, an extruder, to effectively uniformly mix the aliphatic polyester polymer, the polyolefin polymer, and the compatibilizer such that an essentially homogeneous melted mixture is formed. The essentially homogeneous melted mixture may then be cooled and pelletized. Alternatively, the three components may be fed directly into a mixer, such as an extruder, for mixing. They may be added simultaneously or in sequential order. If they are added sequentially, the order in which they are added may be selected as desired. Additionally, the essentially homogeneous melted mixture may be sent directly to a spin pack or other equipment for forming fibers or a nonwoven structure.
The thermoplastic compositions are generally melt blended at a processing temperature that is between about 60xc2x0 C. to about 500xc2x0 C. Desirably, the compositions are formed at a temperature that is between about 80xc2x0 C. to about 300xc2x0 C. Even more desirably, the compositions are formed at a temperature that is between about 100xc2x0 C. to about 250xc2x0 C. and most desirably, the compositions are formed at a temperature that is between about 120xc2x0 C. to about 180xc2x0 C.
It is generally desired that the melting or softening temperatures of the thermoplastic composition be within a range that is typically encountered in most process applications. As such, it is generally desired that the melting or softening temperatures of the thermoplastic composition beneficially be between about 20xc2x0 C. to about 500xc2x0 C., more beneficially be between about 40xc2x0 C. to about 300xc2x0 C., and suitably be between about 50xc2x0 C. to about 200xc2x0 C.
The present invention also includes methods for making a multi-component fiber which is prepared from the thermoplastic composition previously described. For purposes of illustration only, the present description will generally be in terms of a multi-component fiber comprising only three components. However, it should be understood that biodisintegratable non-woven materials made by the present invention may include fibers with three or more components. In one embodiment, the thermoplastic composition may be used to form the sheath of a multi-component fiber while a polyolefin, such as polypropylene or polyethylene, is used to form the core. Suitable structural geometries for multi-component fibers include pie shape or side by side configurations.
With the aliphatic polyester polymer forming a substantially continuous phase, the aliphatic polyester polymer will generally provide an exposed surface on at least a portion of the multi-component fiber which will generally permit thermal bonding of the multi-component fiber to other fibers which may be the same or different from the multi-component fiber. As a result, the multi-component fiber can then be used to form thermally bonded fibrous non-woven structures such as a non-woven web. The polyolefin microfibers in the multi-component fiber generally provide strength or rigidity to the multi-component fiber and, thus, to any non-woven structure comprising the multi-component fiber. To provide such strength or rigidity to the multi-component fiber, it is generally desired that the polyolefin microfibers be substantially continuous along the length of the multi-component fiber.
Typical conditions for thermally processing the various components include using a shear rate that is beneficially between about 100 secondsxe2x88x921 to about 10000 secondsxe2x88x921, more beneficially between about 500 secondsxe2x88x921 to about 5000 secondsxe2x88x921, suitably between about 1000 secondsxe2x88x921 to about 2000 secondsxe2x88x921, and most suitably at about 1000 secondsxe2x88x921. Typical conditions for thermally processing the components also include using a temperature that is beneficially between about 100xc2x0 C. to about 500xc2x0 C., more beneficially between about 150xc2x0 C. to about 300xc2x0 C., and suitably between about 175xc2x0 C. to about 250xc2x0 C.
Methods for making multi-component fibers are also included in the present invention. The melt spinning of polymers includes the production of continuous filament, such as spunbond or meltblown, and non-continuous filament, such as staple and short-cut fibers, structures. To form a spunbond or meltblown fiber, generally, a thermoplastic composition is extruded and fed to a distribution system where the thermoplastic composition is introduced into a spinneret plate. The spun fiber is then cooled, solidified, and drawn by an aerodynamic system, to be formed into a conventional non-woven. Meanwhile, to produce short-cut or staple fiber, rather than being directly formed into a non-woven structure, the spun fiber is cooled, solidified, and drawn, generally by a mechanical rolls system, to an intermediate filament diameter and collected. Subsequently, the fiber may be xe2x80x9ccold drawnxe2x80x9d at a temperature below its softening temperature, to the desired finished fiber diameter and crimped or texturized and cut into a desirable fiber length.
The process of cooling the extruded thermoplastic composition and/or fiber to ambient temperature is preferably performed using a non-water cooling means. Since the compositions include water-soluble components, it is desired to use cooling means that do not include water. Cooling is usually achieved by blowing ambient or sub-ambient temperature air over the extruded polymer. It can be referred to as quenching or super-cooling because the change in temperature is usually greater than 100xc2x0 C. and most often greater than 150xc2x0 C. over a relatively short time frame (seconds).
Multi-component fibers can be cut into relatively short lengths, such as staple fibers which generally have lengths in the range of about 25 to about 50 millimeters and short-cut fibers which are even shorter and generally have lengths less than about 18 millimeters. See, for example, U.S. Pat. No. 4,789,592 to Taniguchi et al, and U.S. Pat. No. 5,336,552 to Strack et al., both of which are incorporated herein by reference in their entirety.
The resultant multi-component fibers are desired to exhibit an improvement in hydrophilicity, evidenced by a decrease in the contact angle of water in air. The contact angle of water in air of a fiber sample can be measured as either an advancing or, a receding contact angle value because of the nature of the testing procedure. The advancing contact angle generally measures a material""s initial response to a liquid, such as water. The receding contact angle generally gives a measure of how a material will perform over the duration of a first insult, or exposure to liquid, as well as over following insults. A lower receding contact angle means that the material is becoming more hydrophilic during the liquid exposure and will generally then be able to transport liquids more consistently. The receding contact angle data is used to establish the highly hydrophilic nature of a multi-component fiber made by the present invention although it is preferable that a decrease in the advancing contact angle of the multi-component fiber also takes place.
Thus, in one embodiment, it is desired that the thermoplastic composition or a multi-component fiber exhibit a Receding Contact Angle value that is beneficially less than about 55 degrees, more beneficially less than about 40 degrees, suitably less than about 25 degrees, more suitably less than about 20 degrees, and most suitably less than about 10 degrees, wherein the receding contact angle is determined by the method that is described in the Test Methods section herein.
Typical aliphatic polyester-based materials often undergo heat shrinkage during downstream thermal processing. The heat-shrinkage mainly occurs due to the thermally-induced chain relaxation of the polymer segments in the amorphous phase and incomplete crystalline phase. To overcome this problem, it is generally desirable to maximize the crystallization of the material before the bonding stage so that the thermal energy goes directly to melting rather than to allow for chain relaxation and reordering of the incomplete crystalline structure. The typical solution to this problem is to subject the material to a heat-setting treatment. As such, when prepared materials, such as fibers, are subjected to heat-setting upon reaching a bonding roll, the fibers won""t substantially shrink because such fibers are already fully or highly oriented. The present invention alleviates the need for this additional processing step because of the morphology of the multi-component fiber. As discussed earlier, the polyolefin microfibers generally provide a reinforcing structure which minimizes the expected heat shrinkage of the aliphatic polyester.
In one embodiment, it is desired that the non-woven material utilize a thermoplastic composition or a multi-component fiber which exhibits an amount of shrinking, as quantified by a Heat Shrinkage value, at a temperature of about 100xc2x0 C., that is beneficially less than about 10 percent, more beneficially less than about 5 percent, suitably less than about 2 percent, and more suitably less than about 1 percent, wherein the amount of shrinking is based upon the difference between the initial and final lengths of a fiber divided by the initial length multiplied by 100. The method by which the amount of shrinking that a fiber exhibits may be determined is included in the Test Methods section herein.
The resultant thermoplastic composition and multi-component fibers may be used to form biodisintegratable non-woven materials that exhibit an increase in high contact angle hysteresis values, quicker intake times for insults, and improved skin dryness, while also keeping very high wetting rates.
The biodisintegratable non-woven materials are suited for use in disposable products including disposable absorbent products such as diapers, adult incontinent products, and bed pads; in catamenial devices such as sanitary napkins, and tampons; and other absorbent products such as wipes, bibs, wound dressings, and surgical capes or drapes. Accordingly, in another aspect, the present invention relates to methods for making a disposable absorbent product comprising the non-woven material previously described.
In one embodiment of the present invention, the multi-component fibers are formed into a fibrous matrix for incorporation into a disposable absorbent product. A fibrous matrix may take the form of, for example, a fibrous non-woven web. Fibrous non-woven webs may be made completely from the multi-component fibers or they may be blended with other fibers. The length of the fibers used may depend on the particular end use contemplated. Where the fibers are to be degraded in water as, for example, in a toilet, it is advantageous if the lengths are maintained at or below about 15 millimeters.
In one embodiment of the present invention, a disposable absorbent product is provided, which disposable absorbent product generally comprises a composite structure including a liquid-permeable topsheet, a fluid acquisition layer, an absorbent structure, and a liquid-impermeable backsheet, wherein at least one of the liquid-permeable topsheet, the fluid acquisition layer, or the liquid-impermeable backsheet comprises the nonwoven material of the present invention. In some instances, it may be beneficial for all three of the topsheet, the fluid acquisition layer, and the backsheet to comprise the nonwoven material made by the present invention.
In another embodiment, the disposable absorbent product may comprise generally a composite structure including a liquid-permeable topsheet, an absorbent structure, and a liquid-impermeable backsheet, wherein at least one of the liquid-permeable topsheet or the liquid-impermeable backsheet comprises the nonwoven material made by the present invention.
In another embodiment of the present invention, the nonwoven material may be prepared on a spunbond line. Resin pellets comprising the thermoplastic materials previously described are formed and predried. Then, they are fed to a single extruder. The fibers may be drawn through a fiber draw unit (FDU) or air-drawing unit onto a forming wire and thermally bonded. However, other methods and preparation techniques may also be used.
Exemplary disposable absorbent products are generally described in U.S. Pat. No. 4,710,187; U.S. Pat. No. 4,762,521; U.S. Pat. No. 4,770,656; and U.S. Pat. No. 4,798,603; which references are incorporated herein by reference.
Absorbent products and structures made according to all aspects of the present invention are generally subjected, during use, to multiple insults of a body liquid. Accordingly, the absorbent products and structures are desirably capable of absorbing multiple insults of body liquids in quantities to which the absorbent products and structures will be exposed during use. The insults are generally separated from one another by a period of time.
Melting Temperature
The melting temperature of a material was determined using differential scanning calorimetry. A differential scanning calorimeter, under the designation Thermal Analyst 2910 Differential Scanning Calorimeter, which was outfitted with a liquid nitrogen cooling accessory and used in combination with Thermal Analyst 2200 analysis software (version 8.10) program, both available from T.A. Instruments Inc. of New Castle, Del., was used for the determination of melting temperatures.
The material samples tested were either in the form of fibers or resin pellets. It was preferred to not handle the material samples directly, but rather to use tweezers and other tools, so as not to introduce anything that would produce erroneous results. The material samples were cut, in the case of fibers, or placed, in the case of resin pellets, into an aluminum pan and weighed to an accuracy of 0.01 mg on an analytical balance. If needed, a lid was crimped over the material sample onto the pan.
The differential scanning calorimeter was calibrated using an indium metal standard and a baseline correction performed, as described in the manual for the differential scanning calorimeter. A material sample was placed into the test chamber of the differential scanning calorimeter for testing and an empty pan is used as a reference. All testing was run with a 55 cubic centimeter/minute nitrogen (industrial grade) purge on the test chamber. The heating and cooling program was a 2 cycle test that begins with equilibration of the chamber to xe2x88x9275xc2x0 C., followed by a heating cycle of 20xc2x0 C./minute to 220xc2x0 C., followed by a cooling cycle at 20xc2x0 C./minute to xe2x88x9275xc2x0 C., and then another heating cycle of 20xc2x0 C./minute to 220xc2x0 C.
The results were evaluated using the analysis software program wherein the glass transition temperature (Tg) of inflection, endothermic and exothermic peaks were identified and quantified. The glass transition temperature was identified as the area on the line where a distinct change in slope occurs and then the melting temperature is determined using an automatic inflection calculation.
Apparent Viscosity
A capillary rheometer, under the designation Gxc3x6ttfert Rheograph 2003 capillary rheometer, which was used in combination with WinRHEO (version 2.31) analysis software, both available from Gxc3x6ttfert Company of Rock Hill, S.C., was used to evaluate the apparent viscosity Theological properties of material samples. The capillary rheometer setup included a 2000 bar pressure transducer and a 30 mm length/30 mm active length/1 mm diameter/0 mm height/180xc2x0 run in angle, round hole capillary die.
If the material sample being tested demonstrated or was known to have water sensitivity, the material sample was dried in a vacuum oven above its glass transition temperature, i.e. above 55 or 60xc2x0 C. for poly(lactic acid) materials, under a vacuum of at least 15 inches of mercury with a nitrogen gas purge of at least 30 standard cubic feet per hour for at least 16 hours.
Once the instrument was warmed up and the pressure transducer was calibrated, the material sample was loaded incrementally into the column, packing resin into the column with a ramrod each time to ensure a consistent melt during testing. After material sample loading, a 2 minute melt time preceded each test to allow the material sample to completely melt at the test temperature. The capillary rheometer took data points automatically and determined the apparent viscosity (in Pascalxc2x7second) at 7 apparent shear rates (in secondxe2x88x921): 50, 100, 200, 500, 1000, 2000, and 5000. When examining the resultant curve it was important that the curve be relatively smooth. If there were significant deviations from a general curve from one point to another, possibly due to air in the column, the test run was repeated to confirm the results.
The resultant rheology curve of apparent shear rate versus apparent viscosity gives an indication of how the material sample will run at that temperature in an extrusion process. The apparent viscosity values at a shear rate of at least 1000 secondxe2x88x921 are of specific interest because these are the typical conditions found in commercial fiber spinning extruders.
Molecular Weight
A gas permeation chromatography (GPC) method was used to determine the molecular weight distribution of samples, such as of poly(lactic acid) whose weight average molecular weight (MW) is between about 800 to about 400,000.
The GPC was set up with two PL gel Mixed K linear 5 micron, 7.5xc3x97300 millimeter analytical columns in series. The column and detector temperatures were 30xc2x0 C. The mobile phase was high-performance liquid chromatography (HPLC) grade tetrahydrofuran (THF). The pump rate was 0.8 milliliter per minute with an injection volume of 25 microliters. Total run time was 30 minutes. It is important to note that new analytical columns must be installed about every 4 months, a new guard column about every month, and a new in-line filter about every month.
Standards of polystyrene polymers, obtained from Aldrich Chemical Co., were mixed into a solvent of dichloromethane(DCM):THF (10:90), both HPLC grade, to obtain 1 mg/mL concentrations. Multiple polystyrene standards could be combined in one standard solution provided that their peaks do not overlap when chromatographed. A range of standards of about 687 to 400,000 molecular weight were prepared. Examples of standard mixtures with Aldrich polystyrenes of varying weight average molecular weights include: Standard 1 (401,340; 32,660; 2,727), Standard 2 (45,730; 4,075), Standard 3 (95,800; 12,860) and Standard 4 (184,200; 24,150; 687).
Next, the stock check standard was prepared. First, 10 g of a 200,000 molecular weight poly(lactic acid) standard, Catalog#19245 obtained from Polysciences Inc., was dissolved to 100 ml of HPLC grade DCM in a glass jar with a lined lid using an orbital shaker (at least 30 minutes). Next, the mixture was poured out onto a clean, dry, glass plate and the solvent allowed to evaporate, then placed in a 35xc2x0 C. preheated vacuum oven and dried for about 14 hours under a vacuum of 25 mm of mercury. Next, the poly(lactic acid) was removed from the oven and the film cut into small strips. Immediately, the samples were ground using a grinding mill (with a 10 mesh screen) taking care not to add too much sample and causing the grinder to freeze up. A few grams of the ground sample were stored in a dry glass jar in a dessicator, while the remainder of the sample can be stored in the freezer in a similar type jar.
It was important to prepare a new check standard prior to the beginning of each new sequence and, because the molecular weight is greatly affected by sample concentration, great care should be taken in its weighing and preparation. To prepare the check standard, 0.0800 gxc2x10.0025 g of 200,000 weight average molecular weight poly(lactic acid) reference standard was weighed out into a clean dry scintillation vial. Then, using a volumetric pipette or dedicated repipet, 2 ml of DCM was added to the vial and the cap screwed on tightly. The sample was allowed to dissolve completely. The sample was swirled on an orbital shaker, such as a Thermolyne Roto Mix (type 51300) or similar mixer, if necessary. To evaluate whether was it dissolved, the vial was held up to the light at a 45xc2x0 angle. The vial was turned slowly and the liquid watched as it flowed down the glass. If the bottom of the vial did not appear smooth, the sample was not completely dissolved. It may take the sample several hours to dissolve. Once dissolved, 18 ml of THF was added using a volumetric pipette or dedicated repipet, the vial capped tightly and mix.
Sample preparations began by weighing 0.0800 gxc2x10.0025 g of the sample into a clean, dry scintillation vial (great care should also be taken in its weighing and preparation). 2 ml of DCM was added to the vial with a volumetric pipette or dedicated repipette and the cap screwed on tightly. The sample was allowed to dissolve completely using the same technique described in the check standard preparation above. Then 18 ml of THF was added using a volumetric pipette or dedicated repipette, the vial capped tightly and mixed.
The evaluation was begun by making a test injection of a standard preparation to test the system equilibration. Once equilibration was confirmed the standard preparations were injected. After those were run, first the check standard preparation was injected and then the sample preparations. The check standard preparation was injected after every 7 sample injections and at the end of testing. Be careful not to take any more than two injections from any one vial, and those two injections must be made within 4.5 hours of each other.
There are 4 quality control parameters to assess the results. First, the correlation coefficient of the fourth order regression calculated for each standard should be not less than 0.950 and not more than 1.050. Second, the relative standard deviation of all the weight average molecular weights of the check standard preparations should not be more than 5.0 percent. Third, the average of the weight average molecular weights of the check standard preparation injections should be within 10 percent of the weight average molecular weight on the first check standard preparation injection. Lastly, record the lactide response for the 200 microgram per milliliter (xcexcg/mL) standard injection on a SQC data chart. Using the chart""s control lines, the response must be within the defined SQC parameters.
Calculate the Molecular statistics based on the calibration curve generated from the polystyrene standard preparations and constants for poly(lactic acid) and polystyrene in THF at 30xc2x0 C. Those are: Polystyrene (K=14.1*105, alpha=0.700) and poly(lactic acid) (K=54.9*105, alpha=0.639).
Heat Shrinkage of Fibers
The required equipment for the determination of heat shrinkage include: a convection oven (Thelco model 160DM laboratory oven, available from Precision and Scientific Inc., of Chicago, Ill.), 0.5 g (+/xe2x88x920.06 g) sinker weights, 1 inch binder clips, masking tape, graph paper with at least 1 inch squares, foam posterboard (11 by 14 inches) or equivalent substrate to attach the graph paper and samples to. The convection oven should be capable of a temperature of about 100xc2x0 C.
Fiber samples are melt spun at their respective spinning conditions. In general, a 30 filament bundle is preferred and mechanically drawn to obtain fibers with a jetstretch ratio of beneficially 224 or higher. Only fibers of the same jetstretch ratio can be compared to one another in regards to their heat shrinkage. The jetstretch ratio of a fiber is the ratio of the speed of the drawdown roll divided by the linear extrusion rate (distance/time) of the melted polymer exiting the spinneret. The spun fiber is usually collected onto a bobbin using a winder. The collected fiber bundle was separated into 30 filaments, if a 30 filament bundle has not already been obtained, and cut into 9 inch lengths.
The graph paper was taped onto the posterboard where one edge of the graph paper was matched with the edge of the posterboard. One end of the fiber bundle was taped, no more than the end 1 inch. The taped end was clipped to the posterboard at the edge where the graph paper was matched up such that the edge of the clip rests over one of the horizontal lines on the graph paper while holding the fiber bundle in place (the taped end should be barely visible as it is secured under the clip). The other end of the bundle was pulled taught and lined up parallel to the vertical lines on the graph paper. Next, at 7 inches down from the point where the clip is binding the fiber, the 0.5 g sinker was pinched around the fiber bundle. The attachment process was repeated for each replicate. Usually, 3 replicates could be attached at one time. Marks could be made on the graph paper to indicate the initial positions of the sinkers. The samples were placed into the oven at a temperature of about 100xc2x0 C. such that the samples hung vertically and did not touch the posterboard. At time intervals of 5, 10 and 15 minutes quickly the new location of the sinkers was marked on the graph paper and samples returned to the oven.
After the testing was complete, the posterboard was removed and the distances between the origin (where the clip held the fibers) and the marks at 5, 10 and 15 minutes were measured with a ruler graduated to {fraction (1/16)} inch. Three replicates per sample is recommended. Calculate averages, standard deviations and percent shrinkage. The percent shrinkage is calculated as (initial lengthxe2x80x94measured length) divided by the initial length and multiplied by 100. As reported in the examples herein and as used throughout the claims, the Heat Shrinkage value represents the amount of heat shrinkage that a fiber sample exhibits at a temperature of about 100xc2x0 C. for a time period of about 15 minutes, as determined according to the preceding test method.
Contact Angle
The equipment includes a DCA-322 Dynamic Contact Angle Analyzer and WinDCA (version 1.02) software, both available from ATI-CAHN Instruments, Inc., of Madison, Wis. Testing was done on the xe2x80x9cAxe2x80x9d loop with a balance stirrup attached. Calibrations should be done monthly on the motor and daily on the balance (100 mg mass used) as indicated in the manual.
Thermoplastic compositions were spun into fibers and the freefall sample (jetstretch of 0) was used for the determination of contact angle. Care should be taken throughout fiber preparation to minimize fiber exposure to handling to ensure that contamination is kept to a minimum. The fiber sample was attached to the wire hanger with scotch tape such that 2-3 cm of fiber extended beyond the end of the hanger. Then the fiber sample was cut with a razor so that approximately 1.5 cm was extending beyond the end of the hanger. An optical microscope was used to determine the average diameter (3 to 4 measurements) along the fiber.
The sample on the wire hanger was suspended from the balance stirrup on loop xe2x80x9cAxe2x80x9d. The immersion liquid was distilled water and it was changed for each specimen. The specimen parameters were entered (i.e. fiber diameter) and the test started. The stage advanced at 151.75 microns/second until it detected the Zero Depth of Immersion when the fiber contacted the surface of the distilled water. From the Zero Depth of Immersion, the fiber advanced into the water for 1 cm and then immediately receded 1 cm. The auto-analysis of the contact angle done by the software determined the advancing and receding contact angles of the fiber sample based on standard calculations identified in the manual. Contact angles of 0 degrees indicate that the sample had become totally wettable. Five replicates for each sample were tested and a statistical analysis for mean, standard deviation, and coefficient of variation percent was calculated. As reported in the examples herein and as used throughout the claims, the Advancing Contact Angle value represents the advancing contact angle of distilled water on a fiber sample determined according to the preceding test method. Similarly, as reported in the examples herein and as used throughout the claims, the Receding Contact Angle value represents the receding contact angle of distilled water on a fiber sample determined according to the preceding test method.
Fluid-Intake and Flowback Evaluation (FIFE)
Fluid-Intake and Flowback Evaluation (FIFE) testing was used to determine the absorbency time and flowback of a personal care product. A Master-Flex Digi-Staltic Automatic Dispensing system was supplied with saline colored with a small amount of FDandC blue dye, set to provide 80 mL insults, and dispensed several times to eliminate any air bubbles. The product samples, infant care diapers, were prepared without elastics so that they would easily lie flat. Two 3.5 inch by 12 inch blotter paper samples were weighed. These papers were placed on the FIFE board, a simple board with a 3 inch by 6 inch raised platform in the middle. The blotter papers were aligned so that they ran lengthwise along either side of the raised platform. The diaper was then aligned so that the area to be insulted was carefully centered on the raised platform, with the topsheet facing up, such that there were no visible wrinkles in the nonwoven topsheet. The second FIFE board was then placed on top of the product. This apparatus consists of a flat board that was intersected by a hollow cylinder, protruding only from the top side of the board. The circular region created where the cylinder intersected the flat plane of the board was hollow. The inner diameter of the cylinder was 5.1 centimeters. A funnel with an inner diameter of 7 millimeters at the short end was placed in the cylinder. The fluid was then dispensed by the pump directly into the funnel. The intake time was recorded by stopwatch from the time the fluid hit the funnel to the moment no fluid was visible on the specimen surface. The blotter papers were checked for product leakage and if any occurred the weight of the blotter papers would have been measured to determine the quantity of fluid that leaked. In the described testing, no leakage occurred. Approximately one minute elapsed before the second insult was applied in the same manner. Again a third insult was applied and timed in the same manner. If desired a procedure may then follow to determine the amount of fluid flowing back when the product is under pressure. In this case, only the intake rates were recorded.
TransEpidermal Water Loss (TEWL)
TransEpidermal Water Loss (TEWL) armband testing was used to measure changes in skin hydration as a result of product use. A lower evaporation value, as measured by a Servo Med Evaporimeter, is indicative of a product that promotes skindryness. This test actually reports a difference in evaporation values. A measurement of moisture evaporation rate is taken prior to the test and then immediately following. The difference in these numbers provides the TEWL value as reported in the results. A lower TEWL value implies that a product provides better breathability to the skin.
Product, in this case infant care diapers, was prepared by hand without any elastics or ears. The basic structure of the diaper was the same, but one control diaper consisted entirely of standard materials and the other had all standard materials except for the topsheet, which was comprised of the biodisintegratable nonwoven. The target area for the insults was drawn in permanent marker on the outside of the product. All testing occurred in a controlled environment of 72xc2x14xc2x0 F. with a relative humidity of 40xc2x15%. The subjects were adult women who were carefully selected to insure that they had no conditions that might potentially alter the results of such a test.
Subjects relaxed in a controlled environment until a stable baseline reading of less than 10 g2/m/hr is obtained with the Servo Med Evaporimeter. These measurements were performed on the inner forearm of the subjects. Masterflex Digi-Staltic batch/dispense pump was used with silicone tubing in the pump head, which was connected to neoprene tubing for dispensing, by barb fittings. The end of the neoprene dispensing tube was placed on the forearm of a subject and the product applied to the forearm with the target insult area directly on top of the tube opening. The product is secured with tape that was wrapped around the diaper and did not contact the skin. The diaper was then loaded with three insults of 60 mL of saline at 45 second intervals and the tube removed. The product was further secured with a stretchable net and the subject required to sit for one hour. After 60 minutes of wear, the product was removed and the Evaporimeter was then used to obtain readings every second for two minutes in the same area on the forearm as the baseline readings were taken. The reported result is the difference between the one-hour and baseline readings.